Not going to be easy, being a 5 window coupe owner since '95. Your best bet is to try Hemmings Motor News. Mine was missing when I bought my coupe. Good luck with your search and keep in touch if you'd like!
28 isnt the same, 31 had pot metal gears, and there always broken, Its a hard piece to find, theres a guy making the gears new, but there pricey and you need the mech to go along with it,